This nonprovisional application claims priority under 35 U.S.C. xc2xa7 119(a) on Patent Application No. 2002-0002060 filed in KOREA on Jan. 14, 2002, which is herein incorporated by reference.
1. Field of the Invention
The present invention relates to a reciprocating compressor, and particularly, to an apparatus for controlling a driving of a reciprocating compressor and a method thereof.
2. Description of the Background Art
Generally, a reciprocating compressor used in a refrigerator or in an air conditioner can control a cooling capacity by varying a compression ratio of the reciprocating compressor with a voltage applied to an inner motor by a user""s intention. The reciprocating compressor will be explained with reference to FIGS. 1 to 3B.
FIG. 1 is a block diagram showing a construction of an apparatus for controlling a driving of a reciprocating compressor in accordance with the conventional art.
As shown in FIG. 1, in the apparatus for controlling a driving of a reciprocating compressor, an inner stroke is varied by receiving a stroke voltage provided by an inner motor (not shown) according to a stroke reference value set by a user, and a cooling capacity is controlled by reciprocating an inner piston (not shown) up and down. The apparatus comprises a voltage detecting unit 30 for detecting a voltage applied to the reciprocating compressor 50 by a variation of the stroke; a current detecting unit 20 for detecting a current applied to the reciprocating compressor 50 by a variation of the stroke; a microcomputer 40 for calculating a stroke by using the voltage and the current detected from the voltage detecting unit 30 and the current detecting unit 20, comparing the calculated stroke with the stroke reference value, and outputting a switching control signal according to the comparison result; and a power supply unit 10 for applying the stroke voltage to the reciprocating compressor 50 by turning on/off an AC power source by using a Triac according to the switching control signal of the microcomputer 40. The stroke of the reciprocating compressor 50 is varied by a voltage applied to the motor according to the stroke reference value set by a user, thereby controlling a cooling capacity by reciprocating the piston up and down. The stroke means a distance that the piston in the reciprocating compressor 50 moves by a reciprocal movement. Hereinafter, operations for controlling a driving of a reciprocating compressor in accordance with the conventional art will be explained.
First, the triac of the power supply unit 10 lengthens a turn-on cycle by the switching control signal of the microcomputer 40, thereby increasing the stroke voltage. At this time, the voltage detecting unit 30 detects a voltage applied to the motor (not shown) in the reciprocating compressor 50, and applies the detected voltage to the microcomputer 40. At the same time, the current detecting unit 20 detects a current applied to the motor (not shown) in the reciprocating compressor 50, and applies the detected current to the microcomputer 40.
Then, the microcomputer 40 calculates a stroke by using the detected voltage and the current from the voltage detecting unit 30 and the current detecting unit 20, compares the calculated stroke with the stroke reference value, and outputs a switching control signal according to the comparison result. That is, when the calculated stroke is smaller than the stroke reference value, the microcomputer 40 lengthens the turn-on cycle of the triac and outputs the switching control signal to the power supply unit, thereby increasing the stroke voltage applied to the reciprocating compressor 50.
Meanwhile, when the calculated stroke is greater than the stroke reference value, the microcomputer 40 shortens the turn-on cycle of the triac and outputs the switching control signal to the power supply unit 10, thereby decreasing the stroke voltage applied to the reciprocating compressor 50.
In the meantime, the lower a cooling capacity is, the higher an efficiency of a refrigerating cycle of a refrigerator or an air conditioner using the reciprocating compressor is. That will be explained with reference to FIGS. 2A to 2B.
FIGS. 2A to 2B show an entire cycle efficiency of a refrigerator using the conventional reciprocating compressor, and an efficiency of the reciprocating compressor.
Referring to FIGS. 2A and 2B, as shown in xe2x80x9cAxe2x80x9d part, an efficiency of the conventional reciprocating compressor used in a refrigerator is lowered when the cooling capacity is varied. Also, when the efficiency of the conventional reciprocating compressor is lowered, as shown in xe2x80x9cA-1xe2x80x9d part, an efficiency of an entire refrigerating cycle of the refrigerator does not increase at a variable cooling capacity where the cooling capacity is varied than at a normal cooling capacity in which the cooling capacity is not varied. That will be explained with reference to FIGS. 3A and 3B.
FIG. 3A shows a waveform for a current and a displacement in a normal cooling capacity of the conventional reciprocating compressor used in a refrigerator.
As shown in FIG. 3A, the reciprocating compressor used in a refrigerator makes a top position (TP) of an inner piston reach up to a top dead center (TDC), a bottom position (BP) of the piston reach up to a bottom dead center (BDC). That is, a compression ratio of the reciprocating compressor in the normal cooling capacity of the refrigerator becomes 100%.
FIG. 3B is a waveform for a current and a displacement when the cooling capacity of the conventional reciprocating compressor used in a refrigerator is varied.
As shown in FIG. 3B, if a user decreases the cooling capacity of a refrigerator in the middle of driving the reciprocating compressor, sizes of the current and the displacement applied to the motor (not shown) in the reciprocating compressor are also decreased. At this time, the current and the displacement do not have a current offset and a displacement offset on the basis of a zero value. That is, in the conventional reciprocating compressor, the cooling capacity is decreased by just decreasing a size of the stroke (the stroke is decreased as a stroke voltage applied to the motor in the reciprocating compressor is decreased). At this time, a dead volume is increased, so that a re-expansion loss is increased, thereby lowering a compressor efficiency. The re-expansion loss means that when the piston of the compressor does not reach up to the top dead center (TDC) (when the cooling capacity is varied), gas in a cylinder of the compressor is not compressed but re-expanded, thereby having a loss. The space which is not compressed is called a xe2x80x9cdead volumexe2x80x9d.
Therefore, an object of the present invention is to provide an apparatus for controlling a driving of a reciprocating compressor and a method thereof, in which a cooling capacity is decreased without a re-expansion loss by controlling a driving of the compressor used in a refrigerator by using a current offset when the cooling capacity of the refrigerator is varied.
Another object of the present invention is to provide an apparatus for controlling a driving of a reciprocating compressor and a method thereof, in which a compressor efficiency and an efficiency of a refrigerating cycle of a cooling apparatus are improved by controlling a driving of the compressor used in a refrigerator by using a current offset when the cooling capacity of a refrigerator is varied.
To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described herein, there is provided an apparatus for controlling a driving of a reciprocating compressor which controls a cooling capacity by varying an inner stroke according to a stroke reference value set by a user, the apparatus comprising a storage unit for storing a current offset value corresponding to a cooling capacity variable amount; an adding unit for adding the current offset value to a current value applied to the compressor in accordance with that the cooling capacity is varied by a user; a microcomputer for generating a switching control signal corresponding to the current value added from the adding unit; and a power supply unit for controlling a driving of the compressor by applying the added current to the compressor under a dependent state on the switching control signal.
To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described herein, there is provided a method for controlling a driving of a reciprocating compressor which controls a cooling capacity by varying an inner stroke according to a stroke reference value set by a user, the method comprising the steps of detecting a current offset value corresponding to a cooling capacity variable amount; adding the current offset value to a current value applied to the compressor in accordance with that the cooling capacity is varied by a user; and applying the added current to the compressor.
The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.